1. Field of the Invention
The present invention relates to a semiconductor device, and more particularly, to a diode having low forward voltage drop (Vf) and preventing recovery breakdown in case of reverse recovery.
2. Description of the Related Art
Recently, a converter bridge having a high power IGBT and a diode disposed in parallel is used for a converter circuit. In the diode, an n− semiconductor layer sandwiched between a p semiconductor layer as an anode and n+ semiconductor layer as a cathode is designed to have long lifetime of carriers in order to decrease the forward voltage. In the event that the lifetime of carriers in the n− semiconductor layer is long like this, recovery current occurred when the diode is switched from the on-state to the off-state (recovery process) is increased. Hereby, there arises a problem that the diode is destroyed during the recovery process (recovery breakdown). Specially, the recovery breakdown is occurred at the peripheral part of the diode where minority carriers are concentrated.
In order to solve the above problem, the following ways are suggested. In the first way, an electron beam is locally irradiated to the peripheral part of the diode where the minority carriers are concentrated so that the lifetime of the carrier is controlled, hereby the breakdown of the diode is prevented (JP, 07-184085, A). In the second way, an anode electrode is disposed so that the edge of the electrode is separated inward from the edge of the p semiconductor layer of anode at the distance of the diffusion length of the minority carrier, hereby the concentration of the minority carriers at the edge of the p semiconductor layer of anode is prevented and the breakdown of the diode is prevented (JP, 3444082).